A strip coiler of a rolling-mill line can be associated with an apparatus including at least two drive or driving rolls for advancing the sheet or strip to the coiler. The apparatus or assembly is particularly intended for hot-rolled strip or strip which is to be heated in the coil and wherein the heated strip is wound by a coiler upon a mandrel.
At least two drive rolls are provided, and these are arranged in parallel and superimposed manner in the stand. The apparatus is also equipped for control of the gap (nip) between the two drive rolls.
The upper drive roll can be connected, via its journal housings, to a swing arm which is associated with cylinders, i.e. piston and cylinder assemblies, which are operated by a pressure medium. These cylinders can serve to adjust the contact pressure or operating force of the rolls. The respective journal housings are held independently of one another at the swing arm, and generally parallel with respect to the direction of movement of this swing arm.
In the hitherto known apparatus for driving or advancing rolled strip or similar product in rolling mills, the upper drive roll is journaled in guides of the respective swing arm, and it can perform floating or similar adjusting movements. The lower drive roll is fixed in position relative to the frame structure, and it is generally disposed in a horizontally aligned attitude.
The relative position of the upper drive roll is determined by two cylinders, i.e. piston and cylinder assemblies, operated with pneumatic pressure. One cylinder is arranged on the drive side of the rolling mill and the other cylinder is provided on the operator's or operating (service) side of the stand of the strip feeder. The cylinders serve to support the upper drive roll such that its central longitudinal axis can be freely adjusted with reference to the strip of material being worked with. These pneumatic cylinders are referred to as control cylinders in the art, and their pressure characteristics can be varied in a smooth and stepless manner.
When the control cylinders are operated with a medium other than compressed air, the minimum contact or operating force is equal to the weight of the upper drive roll. However, it is less when the gap between the drive rolls is of such a magnitude that on initial feeding of strip into the gap only a part of the elastic deflection of the swing arm and of the drive rolls is eliminated in the system.
Especially in the case of thin strip, control of the gap is difficult because minor thickness variations of the strip and other factors can substantially affect the magnitude of the operating or contact pressure. However, based on experience, relatively thin strip needs to be coiled using a low contact pressure to ensure that the strip runs straight.
The operation of the known drive roll apparatus is usually such that the upper drive roll is lifted on introduction of the strip into the gap between the two rolls, and the central longitudinal axis of the upper roll can be freely adjusted or controlled with reference to the strip.
Different friction conditions may prevail at each side, i.e. drive side and service side as mentioned, of the rolling mill at the guide points of the upper roll and the pneumatic cylinders, which can lead to skewing of the upper drive roll on lifting it for initiating strip introduction, and the desired attitude with reference to the strip may not be achieved. This, in turn, may result in an improper course for the strip, i.e. a course which is not straight. A further problem in the known drive roll apparatus is that with reference to the characteristic of the contact force and drive-roll gap, a distance corresponding in magnitude to the play or clearance of the journals of the upper roll must be traversed should the contact force be greater than the weight of the drive roll.
The apparatus described in German Patent Publication (DE-OS) No. 26 14 254 is intended for rolled strip feed, and more particularly for coilers in wide-strip rolling-mill trains. The apparatus includes two drive rolls which are positioned in parallel and superimposed arrangement. The two rolls are adjusted with respect to one another, for preparatory adjustment to various strip thicknesses, to the respective gap distance, by way of a threaded spindle roll height controller.
The upper drive roll is journaled in a swing arm, and the journal housings of this drive roll are held at this arm, but they are independently arranged with respect to one another in such a way that they can be repositioned to carry out the journal functions. The lower or bottom roll, in turn, is guided and journaled by way of balancing devices in the frame, or in the stand.